The invention relates to means for venting a liquid supply system to atmosphere without loss of liquid, particularly but not exclusively a fuel system including a cold starting device for an internal combustion engine.
It is known to provide a diesel-engined argicultural tractor with a fuel system comprising at least one vented tank, a diaphragm pump drawing fuel from the tank and supplying it by way of a filter assembly to a fuel injection pump which delivers it to injectors associated with respective cylinders of the engine, a leak line for returning excess fuel from the fuel injection pump and the injectors to tank, and a cold starting device in the inlet manifold supplied with fuel by gravity from an outlet in the lower part of a reservoir provided in its upper part with an inlet and an outlet by means of which it is interposed in the leak line. A restriction is provided in the leak line upstream of the reservoir, and the major part of the excess fuel may be returned directly from the upstream side of the restriction to the filter assembly to avoid the need for it to pass through the diaphragm pump more than once. A single tank disposed at a higher level than the engine, and two interconnected saddle tanks disposed at a lower level than the engine, have alternatively been employed. There are two reasons why such a system does not always permit the flow of fuel from the reservoir to the cold starting device when necessary. One reason is that when the tank or tanks is or are completely or almost full, the leak line opens below the fuel level therein and air from the tank vent cannot reach the reservoir to enable fuel to flow to the cold starting device. The other reason, which is particularly applicable to tanks disposed below and some distance from the engine, is that even when the tank or tanks is or are partially empty and the leak line opens into a vented air-space above the fuel therein, that part of the leak line between the reservoir and the tank retains oil by capillary action which prevent air from reaching the reservoir to enable fuel to flow to the cold starting device.
One solution to this problem has been to provide a non-return valve for positively venting the reservoir to atmosphere only when a flow of fuel to the cold starting device from the reservoir is required, at which time the system is unpressurised and loss of fuel through the temporary vent does not therefore occur. However, due to the low pressure available to hold the non-return valve closed whilst the engine is running, said valve requires extremely accurate setting.
The object of the present invention is to provide means for permanently and positively venting the reservoir to atmosphere without loss of fuel which require no setting and are very simple and cheap to produce.